One of the non-motor manifestations of PD is visual system involvement. Foveal vision is a main contributor to both visual recognition and discrimination and to both overt and covert visual attention. Experimental evidence from humans and monkeys shows that D1 and D2 receptors are essential for retinal ganglion cell receptive field organization. The evidence linking retinopathy and foveal visual impairment in PD is discussed. A model of retinal preganglionic dopaminergic circuitry is presented. Experimental evidence in humans, using Optical Coherence Tomography shows morphological changes of retinal neurons, including ganglion cells in PD. The diagnosis of pre-cardinal stage of PD (PCPD) may take advantage of the wide availability of optical coherence tomography as a potential biomarker. Fourier-domain OCT and visual testing may contribute a quantitative approach to the early diagnosis, the effects of treatment and follow-up of progression of PD.